In recent decades, GaN and related compounds gained prominence as top semiconductor materials for high-power, high-temperature optoelectronics, electronics, and power conversion. However, better substrate materials are still sought after despite extensive nitride research. Commonly used substrates like sapphire and silicon have high lattice mismatches with GaN, leading to challenges in heteroepitaxial growth.
A promising solution emerged with ScAlMgO4 (SCAM) proposed as a GaN growth substrate. SCAM offers several advantages:
i) Smaller lattice mismatch with GaN than sapphire, reducing dislocation density in grown structures.
ii) Matching thermal expansion coefficient with GaN along the a-axis, reducing residual strain.
iii) Easy cleavage along the c-plane, yielding atomically flat substrates without polishing.
iv) Ability to grow large SCAM crystals via the Chochralski method.
In this study1, we present experimental and theoretical investigations on the optical, electronic, and structural properties of ScAlMgO4. Our experimental techniques include variable angle spectroscopic ellipsometry, optical transmission, X-ray diffraction, scanning electron microscopy, and Raman spectrosco
Cubic ZnxMg1-xO have been proposed as wide bandgap semiconductors for short wavelength optoelectronic applications operating in the deep UV region. By combing MBE growth and HRTEM we were able to determine conditions in which ZnO and ZnxMg1-xO alloys in the rocksalt phase can be grown on MgO substrates. It was found that the maximum ZnxMg1-xO layer thickness strongly depends on Zn concentration, decreasing with x, which reflects the alloy phase instability.
The band structures of rocksalt ZnxMg1-xO alloys were calculated in a supercell geometry by density functional theory in the Local Density Approximation (LDA). The atomic coordinates were determined using pseudopotentials implemented in the VASP Simulation Package. Then, the band structures were obtained by a Linear-Muffin-Tin-Orbital method in a full-potential version with a semi-empirical correction (LDA+C) for the band gaps.
As MgO in the rocksalt structure has a direct band gap and ZnO has an indirect one, we expected transition: direct to the indirect gap for a certain content, x, of Zn.
However, it is shown, that the ZnxMg1-xO band gaps depend strongly on the local arrangement of atoms in a 64 atoms supercell. For each concentration of Zn we obtained a set of the band gap values depending on the arrangement of atoms. Instead of two crossing lines illustrating the dependence of the direct and indirect gaps on composition, we got two crossing bands. The crossing of the two bands covers composition from 10% of Zn up to almost 70% of Zn. The results are compared with the experimental data.
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